You can reach David Wittig by emailing him.
He posts previews of upcoming photo projects on Instagram.
His occasional writings, news, and other miscellany can be found on on his Facebook page.
On Twitter he posts quotes and articles he's currently thinking about, and is usually the first place to have announcements about his work - unless it was a major announcement...
Those go out first to his mailing list which he considers his most loyal followers.
(Though he doesn't like that word, nor the word "fans," but "interesting people who share a common interest in DW's work" is too long to use frequently).